Tilt-wing aircraft

ABSTRACT

In various embodiments, a tilt-wing aircraft includes a fuselage; a first wing tiltably mounted at or near a forward end of the fuselage; and a second wing rotatably mounted to the fuselage at a position aft of the first wing. A first plurality of rotors is mounted on the first wing at locations on or near a leading edge of the first wing, with two or more rotors being mounted on wing portions on each side of the fuselage; and a second plurality of rotors mounted on the second wing at locations on or near a leading edge of the second wing, with two or more rotors being mounted on wing portions on each side of the fuselage. A flight control system generates a set of actuators and associated actuator parameters to achieve desired forces and moments.

CROSS REFERENCE TO OTHER APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationNo. 62/401,032 entitled TILT-WING AIRCRAFT filed Sep. 28, 2016 which isincorporated herein by reference for all purposes.

BACKGROUND OF THE INVENTION

Fixed wing aircraft typically require relatively long runways to takeoff and land. Helicopters do not require runways, but typically theyhave relatively complicated rotors and associated control systems, toenable the aircraft to take off and land and also to fly in forwardflight (e.g., collective and cyclic rotor pitch controls).

Existing vertical takeoff and landing (VTOL) aircraft may be too heavyand complicated for uses such as a personal aircraft.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the invention are disclosed in the followingdetailed description and the accompanying drawings.

FIG. 1A is a diagram showing in perspective view an embodiment of atilt-wing aircraft.

FIG. 1B is a diagram showing the tilt-wing aircraft of FIG. 1A withwings in a forward flight position.

FIG. 2 is a block diagram illustrating an embodiment of a flight controlsystem.

FIG. 3 is a state diagram illustrating transitions of a tilt-wingaircraft in various embodiments.

FIG. 4 is a flow chart illustrating an embodiment of a process tocontrol flight of a tilt-wing aircraft through a transition betweenvertical and forward flight.

FIGS. 5A, 5B, and 6 show variations to the aircraft 100 of FIGS. 1A and1B.

FIG. 7 is a block diagram illustrating an embodiment of a tilt-wingaircraft.

DETAILED DESCRIPTION

The invention can be implemented in numerous ways, including as aprocess; an apparatus; a system; a composition of matter; a computerprogram product embodied on a computer readable storage medium; and/or aprocessor, such as a processor configured to execute instructions storedon and/or provided by a memory coupled to the processor. In thisspecification, these implementations, or any other form that theinvention may take, may be referred to as techniques. In general, theorder of the steps of disclosed processes may be altered within thescope of the invention. Unless stated otherwise, a component such as aprocessor or a memory described as being configured to perform a taskmay be implemented as a general component that is temporarily configuredto perform the task at a given time or a specific component that ismanufactured to perform the task. As used herein, the term ‘processor’refers to one or more devices, circuits, and/or processing coresconfigured to process data, such as computer program instructions.

A detailed description of one or more embodiments of the invention isprovided below along with accompanying figures that illustrate theprinciples of the invention. The invention is described in connectionwith such embodiments, but the invention is not limited to anyembodiment. The scope of the invention is limited only by the claims andthe invention encompasses numerous alternatives, modifications andequivalents. Numerous specific details are set forth in the followingdescription in order to provide a thorough understanding of theinvention. These details are provided for the purpose of example and theinvention may be practiced according to the claims without some or allof these specific details. For the purpose of clarity, technicalmaterial that is known in the technical fields related to the inventionhas not been described in detail so that the invention is notunnecessarily obscured.

A tilt-wing aircraft that efficiently transitions to forward flight isdisclosed. In various embodiments, one or more of a set of rotors/fansmay be positioned in a housing that directs flow over a wing and/or anaerodynamic control surface in a manner that ensures a required liftand/or thrust is provided. In some embodiments, air flow is directedover a wing during a transition from vertical/short take off to forwardflight.

FIG. 1A is a diagram showing in perspective view an embodiment of atilt-wing aircraft. In the example shown, tilt-wing aircraft 100includes a fuselage 102 and a cabin section 104. A forward wing 106 andan aft wing 108 are rotatably mounted to the fuselage 102. In variousembodiments, motors and coupling mechanisms not shown in FIG. 1A areprovided and used under control of a flight control system (not shown)to rotate wings 106 and 108 from the vertical position, as shown in FIG.1A, to a forward flight position, as shown in FIG. 1B. Forward wing 106and aft wing 108 each have four electric motor-driven rotors (also knownin various embodiments as “fans”, “lift fans”, or “propellers”) 110mounted thereon, two on each side of fuselage 102. In the example shown,rotors 110 are mounted in a fixed position relative to the wings 106,108, on a leading edge of wings 106, 108.

In various embodiments, rotors 110 may be driven by electric motors (notshown) mounted adjacent to each rotor 110. Electric motors are wellsuited to a distributed propulsion application where a plurality ofsmall motors are used to drive small, high RPM, propellers as opposed tofewer high power motors driving larger and slower propellers. Whileinternal combustion engines get more efficient at large scale, smallelectric motors can be make very efficient and light weight. They arealso composed of a small number of moving parts and are therefore veryrobust. In various embodiments, use of electric motors to drive rotors110 of aircraft 100 enables a smaller, lighter weight VTOL aircraft tobe provided.

In the example shown in FIGS. 1A and 1B, each rotor 110 is surrounded bya housing 112. In the example shown, the respective housings 112 areshown as being mounted and partly integrated into the leading edge ofwings 106, 108. In various embodiments, the housings 112 may serve toprotect a pilot or other user of aircraft 100 from accidental contactwith rotors 110, or piece or other debris that may be thrown by rotors110. In some embodiments, the housing 112 may extend further into (i.e.,in the direction of a trailing edge) of the wings 106, 108. The housing112 may function as an inlet/intake structure, directing the flow of airinto the rotors 110. In some embodiments, a portion of housing 112 mayextend beyond a trailing edge/side of the rotor 110, i.e., the rotoroutlet side, and may be shaped and/or positioned to direct airflowgenerated by the rotor 110 over the wing 106, 108 and/or an aerodynamiccontrol surface, such as an aileron, position at or near a trailing edgeof the wing. In various embodiments, the aileron or other controlsurface may be manipulated under control of a flight control system ofthe tilt-wing aircraft, e.g., to achieve or maintain a desired (e.g.,minimum) amount and/or direction of lift, for example as the aircrafttransition to forward flight mode.

In the example shown in FIG. 1, the forward and aft wings 106, 108 areapproximately equal in length. A tandem wing design where both theforward (front) wing, sometimes called a “canard”, and aft wing carrysubstantial portions of the total lift is well suited for a small,compact, vertical or short takeoff vehicle. The structure of the twowings allows mounting points for a plurality of motors that can bedistributed in a way that the geometric center of the motors is close tothe airplane center of gravity, therefore providing efficient loaddistribution and better resilience to potential motor failure. Moreover,while a traditional horizontal tail usually requires a larger airplanelength, a tandem wing airplane is typically shorter in length. This typeof wing arrangement also provides good aerodynamic efficiency at highspeed and can generally be designed such that the stall characteristicsare good.

FIG. 2 is a block diagram illustrating an embodiment of a flight controlsystem. In the example shown, flight control system 200 includes a setof inceptors 202, such as throttle, stick, or other manual inputdevices, configured to generate a set of inceptor inputs 204, e.g., aset of roll, pitch, yaw, and/or throttle commands or signals. Acontroller 206 interprets the inceptor inputs 204 and computes andprovides as output a corresponding set of forces and moments 208. Forexample, forces in and moments about each of three axes (e.g., x(forward direction/roll), y (side direction/pitch), and z (verticaldirection/yaw) may be provided.

A control mixer 210 receives force/moments 208 and generates a set ofactuators and actuator parameters 212, which are provided to actuators214 to maneuver and propel the aircraft. Examples of actuators include,without limitation, rotors, fans, and propellers, such as rotors 110 ofFIGS. 1A and 1B, and aerodynamic control surfaces, such as ailerons,elevators, and rudders. For example, each of the rotors 110 in theexample shown in FIGS. 1A and 1B may receive a corresponding thrust(speed) command, to control the attitude of the aircraft (e.g.,orientation relative to horizontal or ground) and the speed of theaircraft in one or more directions (e.g., upward during vertical flightmode, as during takeoff, or forward in forward flight).

In the example shown in FIG. 2, control mixer 210 receives from one ormore sensors 216 sensor data 218. In various embodiments, the sensordata 218 may be used by control mixer 210 to determine theactuators/parameters 212 to be provided as output to achieve (to anextent practical) a requested set of forces/moments 208. For example,air temperature, electric motor temperature, airspeed of the aircraft,etc. may be measured by sensors 216 and provides as sensor data 218.Such sensor data may be used by control mixer 210 to determine whichactuators are available and/or for each its effectiveness under thesensed conditions indicated by the sensor data 218.

In various embodiments, flight control system 200 comprises one or moreprocessors configured to perform the processing and control functionsdescribed above as being performed by the controller 206 and/or controlmixer 210.

FIG. 3 is a state diagram illustrating transitions of a tilt-wingaircraft in various embodiments. In various embodiments, a flightcontrol system such as the flight control system 200 of FIG. 2 may beconfigured to control the actuators (rotors, aerodynamic controlsurfaces) of the aircraft to cause the aircraft to transition betweenand operate within operational states or modes as shown in FIG. 3.

In the example shown, the aircraft may transition from groundmode/stopped state 302 through a takeoff transition/sequence 304 toenter a vertical (or short) takeoff mode/state 306. An example of atilt-wing aircraft in takeoff mode 306 is shown in FIG. 1A. From thetakeoff mode 306, the aircraft may transition via a vertical-to-forwardflight transition 308 to a forward flight mode 310. An example of atilt-wing aircraft in forward flight mode 310 is shown in FIG. 1B.

From vertical takeoff mode 306 a transition 312 directly to verticallanding mode 316 may be made. Alternatively, vertical landing mode 316may be entered from forward flight mode 310 via transition 314. Forexample, a button or other control to initiate landing may be activatedby the pilot. In various embodiments, a tilt-wing aircraft in verticallanding mode 316 appears as shown in FIG. 1A, i.e., wings rotated tovertical flight position.

From the vertical landing mode 316, the aircraft transitions via alanding approach/sequence 318 back to the ground mode 302.

FIG. 4 is a flow chart illustrating an embodiment of a process tocontrol flight of a tilt-wing aircraft through a transition betweenvertical and forward flight. In the example shown, an indication totransition to forward flight is received (402). In response, atransition to forward flight is initiated and forward airspeed begins tobe monitored (404). A combined lift generated by the aircraft's rotorsand wings is computed/updated continuously (406). For example, as thewings are tilted to the horizontal position for forward flight and asforward speed of the aircraft through the air increases, the liftgenerated by the wings may increase while the lift generated by therotors may decreases absent changes to the rotor torque (and/or speed,thrust, etc.). If an insufficient lift condition is detected (408),rotor torque and/or pitch may be adjusted to compensate (410), e.g., togenerate a higher upward force component. Variable pitch propellers(rotors) have a mechanism that allows dynamically changing the incidenceof the blades. This allows such a propeller to generate thrust moreefficiently through a wide range of airspeeds. This characteristic of avariable pitch propeller (rotor) may be especially relevant for a VTOLor STOL airplane that operates over a wide range of airspeeds. If arotor stall condition is detected (412), rotor pitch may be adjusted tocompensate (414). Adjustments to rotor torque and/or pitch are made, asrequired, until the transition to forward flight has been completed(416), e.g., the wings have been rotated fully to the horizontalposition, and forward airspeed is sufficient for the wings to generatesufficient lift to maintain altitude.

For variable pitch rotors, thrust can be increased either by changingrotor RPM or by changing rotor pitch or a combination of both.Advantages of using pitch for actuation include the fact that it can bevery fast to respond to commands. Most notably, it allows fast actuatorresponse around zero thrust and allows the rotor to quickly generatenegative thrust without reversing RPM. This can be used to generatedesired moments in roll, pitch or yaw about the vehicle center ofgravity.

In various embodiments, the aircraft control system commands both rotorspeed and pitch to ensure fast actuator response as well as efficient,low power, operation.

In some embodiments, the variable pitch system is slow so that weight isminimized. Consequently, rotor pitch is not commanded to vary at highbandwidth but slowly changed based on sensor readings such as airspeedto allow for efficient operations and increase the achievable maximumairspeed. In that case, high bandwidth actuation is achieved by varyingRPM.

FIG. 4 is an example of a control system that may be used in variousembodiments to transition a tilt-wing aircraft as disclosed hereinbetween vertical (e.g., takeoff, landing, and/or hover) and forwardflight. In various embodiments, one or more portions of the process ofFIG. 4 may be omitted. For example, steps 412 and 414 may be omitted insome embodiments. In some embodiments, transition to forward flight maybe effected by attaining a desired (e.g., design minimum or greater)altitude and rotating the wings substantially continuously to a forwardflight position, while adjusting power to the rotors as required tomaintain stability and altitude while increasing forward airspeed as thewings are rotated into the forward flight position and begin to generatesufficient lift to maintain altitude.

FIGS. 5A, 5B, and 6 show variations to the aircraft 100 of FIGS. 1A and1B. In the aircraft 500 of FIG. 5A, the tail structures shown in FIGS.1A and 1B as being position on each outer end of the aft wing 108 hasbeen replaced with a single, centrally located tail 502. The aircraft540 of FIG. 5B does not include a tail structure and omits theducts/shrouds around the rotors. Yaw control is maintained by using aflight control system to vary rotor speed/torque as required.

In the aircraft 600 of FIG. 6, the tail structures shown in FIGS. 1A and1B as being position on each outer end of the aft wing 108 have beenaugmented 602 to extend below the aft wing 108, in addition to above.

In various embodiments disclosed herein, ducts/shrouds may be includedor not, depending on the extent to which such ducts/shrouds may berequired or desired for safety, e.g., to prevent human contact withrotor blades, and/or to direct flow, e.g., across a control surface.Likewise, tail structures may be included or not, as desired. In variousembodiments, features shown in a given embodiment may be mixed andmatched with features shown in one or more other embodiments to providea tilt wing aircraft within the scope of the present disclosure. Inaddition, while a number of aircraft shown in the figures and/ordescribed herein have eight rotors, i.e., two per wing, in variousembodiments more or fewer rotors may be included, such fewer (e.g., 4)or more (e.g., 10, 12, etc.) rotors. While in some embodiments, controlsurfaces such as ailerons and rudders, are shown, in various embodimentsother or different control surfaces may be included and/or such controlsurfaces may be omitted entirely and a flight control system may be usedto maintain aircraft stability and position (attitude) using only therotors.

FIG. 7 is a block diagram illustrating an embodiment of a tilt-wingaircraft. In the example shown, the aircraft 700 includes structuressimilar to those shown in FIGS. 1A and 1B. Each of the wings 704 and 706affixed to fuselage 702 has a set of four housings 708 and associatedrotor assemblies 710, comprising rotors and associated electric motors.In addition, behind each housing 708 and rotor assembly 710, there is arotor-specific aerodynamic control surface 712. In various embodiments,each of the eight aerodynamic control surfaces 712 is independentlycontrolled. Each may be positioned at an assigned angle relative to thewing 704, 706, e.g., to control and/or direct flow from the associatedrotor assembly 710 over the portion of the wing on which the controlsurface 712 is mounted and/or to control, for a given speed or torque ofthe rotor assembly 710 an amount and/or direction of lift that isgenerated and/or contributed.

In some embodiments, in vertical flight modes, the control surfaces 712may be used to provide attitude control, e.g., yaw control, bydeflecting the airflow (i.e., rotor wash) generated by the associatedrotor assembly 710.

In some embodiments, aircraft control may be achieved with respect toone or more embodiments of a tilt-wing aircraft as disclosed hereinsolely by computing and applying a corresponding thrust or other commandor control input to and/or with respect to each of a plurality of liftfans. In some embodiments, having a forward and aft wing of a tandemwing tilt-wing aircraft, as disclosed in various embodiments describedherein, facilitates control using only lift fans, e.g., by enabling adesired/requested moment about one or more axes, such as a pitch axis,to be applied using only lift fans. In some embodiments, no aerodynamiccontrol surfaces are included on a tilt-wing aircraft as disclosedherein, and only lift fans are used to provide control.

Although the foregoing embodiments have been described in some detailfor purposes of clarity of understanding, the invention is not limitedto the details provided. There are many alternative ways of implementingthe invention. The disclosed embodiments are illustrative and notrestrictive.

What is claimed is:
 1. A tilt-wing aircraft, comprising: a fuselage; afirst wing tiltably mounted at or near a forward end of the fuselage; asecond wing rotatably mounted to the fuselage at a position aft of thefirst wing; wherein the first wing and the second wing each is coupledto the fuselage by a tilt mechanism configured to rotate a wing betweena first position in which the wing is substantially in a verticalorientation with respect to the fuselage and a second position in whichthe wing is substantially in a horizontal orientation with respect tothe fuselage; a first plurality of rotors mounted on the first wing atlocations on or near a leading edge of the first wing, with two or morerotors being mounted on wing portions on each side of the fuselage; asecond plurality of rotors mounted on the second wing at locations on ornear a leading edge of the second wing, with two or more rotors beingmounted on wing portions on each side of the fuselage; and a flightcontrol system configured to determine a set of desired forces andmoments based at least in part on a set of inceptor inputs; receivesensor data; generate, based at least in part on said sensor data andsaid set of desired forces and moments, a set of actuators andassociated actuator parameters the set of actuators being selected froma superset of actuators that includes the first plurality of rotors andthe second plurality of rotors; and provide to each actuator in thegenerated set a corresponding set of one or more actuator parametersgenerated for that actuator.
 2. The tilt-wing aircraft of claim 1,wherein each of said rotors includes a housing configured to directairflow generated by said rotor across an associated aerodynamicsurface.
 3. The tilt-wing aircraft of claim 2, wherein a shape of thehousing directs airflow generated by said rotor across the associatedaerodynamic surface.
 4. The tilt-wing aircraft of claim 3, wherein thehousing comprises an annular outlet duct configured to direct airflowgenerated by said rotor across the associated aerodynamic surface. 5.The tilt-wing aircraft of claim 2, wherein the associated aerodynamicsurface comprises a surface of a corresponding one of the first wing orthe second wing.
 6. The tilt-wing aircraft of claim 2, wherein theassociated aerodynamic surface comprises a movable aerodynamic controlsurface mounted on a trailing edge of a corresponding one of the firstwing or the second wing.
 7. The tilt-wing aircraft of claim 6, whereinthe associated aerodynamic surface comprises an aileron.
 8. Thetilt-wing aircraft of claim 7, wherein the aileron is positioned on atrailing edge of said corresponding one of the first wing or the secondwing at a position directly aft of a corresponding one of said rotors.9. The tilt-wing aircraft of claim 8, wherein the aileron has a widthsuch that the airflow of said corresponding one of said rotors isdirected to flow substantially across the aileron.
 10. The tilt-wingaircraft of claim 9, wherein the width and position are such thatsubstantial airflow of other ones of said rotors is not directed to flowsubstantially across the aileron.
 11. The tilt-wing aircraft of claim 1,wherein the first wing is mounted forward of a center of gravity of thefuselage.
 12. The tilt-wing aircraft of claim 1, wherein the second wingis mounted aft of a center of gravity of the fuselage.
 13. The tilt-wingaircraft of claim 1, wherein the second wing includes on each end avertically oriented tail portion.
 14. The tilt-wing aircraft of claim13, further comprising a rudder positioned at a trailing edge of eachtail portion.
 15. The tilt-wing aircraft of claim 1, wherein the firstplurality of rotors and the second plurality of rotors are each drivenby a corresponding electric motor.
 16. The tilt-wing aircraft of claim1, wherein the superset of actuators includes one or more aerodynamiccontrol surfaces.
 17. The tilt-wing aircraft of claim 1, wherein thefirst plurality of rotors and the second plurality of rotors havevariable pitch rotor blades.
 18. The tilt-wing aircraft of claim 17,wherein the flight control system is further configured to vary a pitchof the first plurality of rotors and the second plurality of rotors. 19.The tilt-wing aircraft of claim 1, wherein the first wing and the secondwing are of comparable length.
 20. The tilt-wing aircraft of claim 1,wherein the first plurality of rotors and the second plurality of rotorsare equal in number.